The goal of this project is to produce large quantities of endothelial cells (EC) which can be readily manipulated to elucidate mechanisms that are central to the understanding of endothelial participation in homeostasis. A secondary endpoint is to demonstrate that cultured endothelia behave similarly to in situ endothelium found in the intima of blood vessels and in the capillaries. The basic assumption upon which the research rests is that EC are the principal receptor sites of a servomechanism between blood and tissue fluid, and that EC communicate with EC and with other types of cells, such as smooth muscle. The experimental focus will be: (1) to profile EC freshly obtained by non-enzymatic procedures and EC at different stages of culturing and subculturing; (2) to observe morphological responses, as determined by electron microscopy, of EC to vasoactive, thrombogenic and pharmacologic (endotoxins) agents; (3) to determine the parameters of calcium flux and storage in EC, and as the possible roles of the cation in regulation; (4) to demonstrate that ions and metabolites pass through intercellular low-resistance channels (gap junctions); (5) to incorporate the significant findings of the in vitro experiments into the experimental system designed for our investigations on platelet-endothelial interaction and the regulation of pulmonary circulation and ventilation as observed in the intact dog.